<style>
    button {
        position: absolute;
        margin: 20px;
    }

    #pause::after {
        content: 'Pause';
    }

    #pause.pause::after {
        content: 'Play';
    }
</style>
<div id="map"></div>
<button id="pause"></button>
<script>
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v11',
        center: [0, 0],
        zoom: 0.5
    });

    // Create a GeoJSON source with an empty lineString.
    var geojson = {
        'type': 'FeatureCollection',
        'features': [
            {
                'type': 'Feature',
                'geometry': {
                    'type': 'LineString',
                    'coordinates': [[0, 0]]
                }
            }
        ]
    };

    var speedFactor = 30; // number of frames per longitude degree
    var animation; // to store and cancel the animation
    var startTime = 0;
    var progress = 0; // progress = timestamp - startTime
    var resetTime = false; // indicator of whether time reset is needed for the animation
    var pauseButton = document.getElementById('pause');

    map.on('load', function() {
        map.addSource('line', {
            'type': 'geojson',
            'data': geojson
        });

        // add the line which will be modified in the animation
        map.addLayer({
            'id': 'line-animation',
            'type': 'line',
            'source': 'line',
            'layout': {
                'line-cap': 'round',
                'line-join': 'round'
            },
            'paint': {
                'line-color': '#ed6498',
                'line-width': 5,
                'line-opacity': 0.8
            }
        });

        startTime = performance.now();

        animateLine();

        // click the button to pause or play
        pauseButton.addEventListener('click', function() {
            pauseButton.classList.toggle('pause');
            if (pauseButton.classList.contains('pause')) {
                cancelAnimationFrame(animation);
            } else {
                resetTime = true;
                animateLine();
            }
        });

        // reset startTime and progress once the tab loses or gains focus
        // requestAnimationFrame also pauses on hidden tabs by default
        document.addEventListener('visibilitychange', function() {
            resetTime = true;
        });

        // animated in a circle as a sine wave along the map.
        function animateLine(timestamp) {
            if (resetTime) {
                // resume previous progress
                startTime = performance.now() - progress;
                resetTime = false;
            } else {
                progress = timestamp - startTime;
            }

            // restart if it finishes a loop
            if (progress > speedFactor * 360) {
                startTime = timestamp;
                geojson.features[0].geometry.coordinates = [];
            } else {
                var x = progress / speedFactor;
                // draw a sine wave with some math.
                var y = Math.sin((x * Math.PI) / 90) * 40;
                // append new coordinates to the lineString
                geojson.features[0].geometry.coordinates.push([x, y]);
                // then update the map
                map.getSource('line').setData(geojson);
            }
            // Request the next frame of the animation.
            animation = requestAnimationFrame(animateLine);
        }
    });
</script>
